The “I Kissed a Girl” hitmaker found fame last year and was away from McCoy for long periods of time as she promoted the track.

And it was allegedly her upcoming hectic tour schedule that prompted the couple’s break, which was announced last week.

A source tells Britain’s News of the World, “It’s sad, but they were fighting a lot in recent months because they never saw each other.

“When somebody becomes very famous very quickly their relationship usually suffers. She’s going through such a huge time at the moment so needs to be on her own.”

McCoy has already gone online to blast his ex in a bitter poem on his Web site: “We fight every night, now that’s not kosher. I reminisce with bliss of when we was closer. And wake up to be greeted by an argument again. You act like you’re 10.”